Aluminum alloy



April 21, 1942- P. T. STROUP 7 ALUMINUM ALLOY Original Filed Oct. 27,1959 ATTORNE" Patented Apr. 21, 1942 2.280.176 I ALUMINUM ALLOY toAluminum Philip '1. Stroup, New Kensington, Pa., assignor ompany ofAmerica, Pittsburgh,

Pa., a corporation of Pennsylvania Original application October 27,1939. Serial No. 301,594. Divided and this application October 1, 1940,Serial No. 359,246

7 3Claims. (01. 15-147) This invention relates to aluminum base a1-loys, and it is .particularly concerned with con- ,trolling the grainsize in castings. This is a divisional applicationof my copendingapplication, Serial No. 301,594, filed October 27, 1939.

. Among the factors which affect the properties and behavior of bothwrought and cast aluminum base alloy articles, one of the most importantis the grain size of the metal. The term grain size refers to thedimensions of the individual crystals which-compose the metallic body.The grain size is usually referred to as being fine, medium, or coarse,and the shape of the grains is described as being equi-axed orelongated, depending upon the relative dimensions of the grain.Generally, a line equi-a'xed grain size is considered to be mostdesirable in an alloy both from the standpoint of strengthand hardness,as well as workability. Since some aluminum base alloys do notinherently exhibit a small grain size in the as-cast condition, and,furthermore, since thermal conditions during solidification of themolten metal exercise such a great influence upon the size of grains, itis necessary to exercise some control of the alloy composition orfreezing conditions in order to insure a uniform structure in theproduct. This need is most apparent inthe J A satisfactory means forcontrolling the size of grains in-aluminum base alloy castings shouldpossess the following characteristics: (1) convenience in application;(2) uniformity in eifect; and (3) a minimum of undesired effect on otherimportant properties.

It is the principal object of my invention to provide a simple means forproducing small equi axed grains in cast aluminum base alloys. Anotherobject is to provide a means for effecting this control 'of grain sizewhich has the abovementioned characteristics. These and other objectswill become apparent from the following description of my invention.

I have discovered that the addition of small amounts of-one or both ofthe elements, columbium and tantalum, to aluminumbase alloys produces asmall grain size in the as-cast product. While the presence of eitherelement alone in an alloy has a pronounced effect upon the grain size,

an even greater effect is obtained if both elements are present. As faras I have observed, the

addition of these elements to aluminum base althese elements issubstantially uniform throughout the entire article.- This uniformity ineffect is particularly advantageous in the casting of ingots or otherarticles of relatively large cross sectional dimension.

Thev benefit derived from adding columbium and/or tantalum to aluminumbase alloys as mentioned hereinabove is particularly evident in thereduction of the grain size of the as-cast metal. However, the additionof these elements may also have other beneficial effects both in thecasting and in the wrought product made from the cast article. Byemphasizing the effect upon the grain size of the cast alloys, I do notwish to minimize any advantages gained in other respects.

Only relatively small amounts of columbium 0.5 per cent, and preferablynot over 0.4 per cent.

Although either element is effective when used separately, 1 have foundthat an even more pronounced grain-refining effect is obtained if bothare simultaneously employed. In such a case the total amount should notbe less than about 0.02

per cent, nor should it exceed about 0.5 per cent.

The elements columbium and tantalum, for the purposes of myjinvention,are regarded as being equivalent to each other, that is, one may besubstituted for the other although not necessarily in the sameproportions, and therefore they constitute a group. In addition tohaving a similar alloy constitutional diagram with aluminum.

The aluminum base alloys which are particularly benefited by th additionof at least one of the elements of the columbium-tantalum group arethose containing from 0.25 to 12 per cent copper, or 0.5 to- 15 per centmagnesium, or 0.25 to 14 per cent silicon, or 0.5 to 20 per cent zinc,

or 0.1 m3 per cent manganese, or combinations of two or more of theseelements. These alloys may also contain one or more of the followingelements, often referred to as hardeners", in the following percentages:0.05 to 0.5 per cent chromium, 0.0l to 0.5 per cent titanium, 0.25 to2.5 per cent nickel, 0.01 to 0.5 per cent boron, 0.002 to 2 per centberyllium, 0.1 to 0.5 percent molybdenum, and 0.1 to 0.5 per centzirconium- The total amount of the latter elements, however,

' should not exceed about 3 per cent. As exemplary of the variety of.alloys whose grain size has been found to be reduced by the addition ofcolumbium and/or tantalum, the following compositions are cited, whereinaluminum constitutes the balance of the alloy in each case: 1.25 percent manganese; 2.5 per cent magnesium, 0.25 per cent chromium; 2 percent Mg2Si, 0.25 per cent chromium; 4 per cent copper; per cent silicon;5.25 per cent MgZnz; 1.25 per cent magnesium, 0.5 per cent zinc, 0.15per cent copper; and 4.4 per cent copper, 0.65 per cent manganese, 1.5per cent magnesium.

The efiect of adding columbium or tantalum, or both elements, to aparticular alloy is illustrated in the accompanying figures, where Fig.1 is a photomicrograph of an as-cast alloy composed of 2.5 per centmagnesium, 0.25 per cent chromium, the balance commercially purealuminum;

Fig. 2 is a photomicrograph of the same alloy to which 0.03 per centcolumbium had been added;

Fig. 3 is a photomicrograph of the same alloy to which 0.06 per centtantalum had been added; and 4 Fig. 4 is a photomicrograph of the samealloy to which 0.02 percent columbium and 0.07 per cent tantalum hadbeen added.

The alloy employed for the test was one which is widely used in wroughtform, and has a nominal composition of 2.5 per cent magnesium, 0.25 percent chromium, and the balance aluminum containing a maximum of 0.3 percent iron and silicon as impurities. A quantity of the alloy was firstmelted and a specimen poured at a temperature of 1350 F. into a cold,thin-walled iron mold having the shape of a' frustum of an inverted conewith a diameter of about three inches atthe base of the cone. About fiveminutes Was required for the metal to completely solidify, which tendedto promote the formation of large grains. The remaining melt was dividedinto three portions, 0.03 per cent columbium being added to one, 0.06per cent tantalum being added to the second, and 0.02 per cent'columbiumand 0.07 per cent tantalum being added to the third. Specimens were castat a temperature of 1350 F. in the same iron mold as the alloy withoutthe columbium 0r tantalum additions, the mold in each case being at roomtemperature, or cold, when the metal was poured into it. The specimenswere sectioned in a vertical plane, polished, and etched in an aqueoussolution of nitric and hydrochloric acids. A representative section ofeach specimen was then photographed at a magnification of threediameters.

In Fig. 1 the large grains of the untreated alloy may be plainly seen.Grains of this size are regarded as being too coarse for a satisfactorycasting ,as well as promoting cracking and checking in a body that is tobe subsequently worked. The criss-cross markings on some of the rainsillustrate a common solidification phenomenon known as dendriticformation. The grain-refining effect of adding columbium to the alloy isseen in Fig. 2. In comparison to Fig. 1, the grains are very small andequi-axed. In Fig. 3, the grain size of the alloy to which tantalum hadbeen added may be seen. Since 0.06 per cent tantalum was employed, ascompared to 0.03 per cent columbium in the preceding example, it is notsurprising that the grain size should be smaller than in Fig. 2. Thevery marked efiect of both columbium and tantalum on the grain size isshown in Fig. 4. The grain size is so small as to be scarcelydistinguishable at a magnification of three diameters, which is the samemagnification that was used in the other photomicrographs.

The tantalum and columbium may be added to molten aluminum base alloysin any convenient manner. I have found that the ferro-alloys of thesetwo elements provide a satisfactory source. The fe'rr-o-alloy ispreferably diluted with aluminum at a high temperature, and this dilutedalloy containing, for example; 2 .to .5 per cent .of columbium or.tantalum is used for making other advantage obtained through usingtheferro-alloys as a source of columbium and tantalum'is that both ofthese elements will usually be present and therefore tend to produce anI even finer structure than if only one is employed.

- In referring to aluminum base alloys herein, I mean those whichcontain at least 50 per cent aluminum. The term aluminum as hereinemployed refers to the metal as commercially produced which containsimpurities.

Where, in the appended claims, the balance of an alloy is said to besubstantially aluminum, it is intended that this expression" shallpermit the inclusion in the .alloy composition of one or more of thehardening elements mentioned hereinabove as well as the usualimpurities.

I claim:-

1. A cast article composed of an aluminum base alloy consisting of from0.25 to 14 per cent silicon, 0.5 to 15 per cent magnesium, at least 0.01per cent each of the metals tantalum and columbium, the total amount ofsaid two metals not exceeding 0.5 per cent, and the balance aluminum.

2. A cast article composed of an aluminum base alloy containing from0.25 to 14 per cent silicon, 0.5 to 15 per cent magnesium, and at least0.01 per cent of each of the metals tantalum and columbium, the totalamount of said two metals not exceeding 0.5 per cent and the balancesubstantially aluminum, said alloy being characterized in theas-castcondition by a finer grain size than the same alloy containing eithertantalum or columbium alone.

3. A cast article composed of an aluminum base alloy consisting of from0.25 to 14 per cent silicon, 0.5 to 15 per cent magnesium, and at leastone of the hardeners of the group composed of 0.05 to 0.5 per centchromium, 0.01 to 0.5 per cent titanium, 0.25 to 2.5 per cent nickel,0.01 to 0.5 per cent boron, 0.002 to 2 per cent beryllium, 0.1 to 0.5per cent molybdenum, and

0.1 to 0.5'per cent zirconium, the total amount of said hardeners notexceeding about 3 per cent.

and at least 0.01 per cent of each of the metals tantalum and columbium,the total amount of said two metals not exceeding 0.5 per cent, thebalance of the alloy being aluminum.

PHILIP T. STROUP.

